Teach ValueHandleBase to treat DenseMap's special Empty and Tombstone values the same way it treats null pointers. This is needed to allow CallbackVH to be used as a key in a DenseMap.
Teach ValueHandleBase to treat DenseMap's special Empty and Tombstone
values the same way it treats null pointers. This is needed to allow
CallbackVH to be used as a key in a DenseMap.


git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@77695 91177308-0d34-0410-b5e6-96231b3b80d8

chubbymaggie/asap,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,chubbymaggie/asap,chubbymaggie/asap,apple/swift-llvm,llvm-mirror/llvm,dslab-epfl/asap,apple/swift-llvm,GPUOpen-Drivers/llvm,chubbymaggie/asap,GPUOpen-Drivers/llvm,chubbymaggie/asap,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,dslab-epfl/asap,llvm-mirror/llvm,chubbymaggie/asap,llvm-mirror/llvm,dslab-epfl/asap,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,dslab-epfl/asap,apple/swift-llvm,dslab-epfl/asap,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm